The present invention relates to a real-time adjustment system for adjusting the radial clearances between rotor and stator elements of a gas turbine engine.
In order to maximize the efficiency and performance of gas turbine engines, specifically those utilized in aircraft, the radial clearances between the rotor and stator elements should be kept to a minimum. However, the clearances must also accommodate radial expansion and contraction of the elements due to changing temperatures of the rotor and stator elements and the changing rotational speeds of the rotor elements. The rotor and stator elements will, of course, radially expand as the temperature increases, while the rotor elements will expand or contract as their rotational speed increases or decreases, respectively.
A variety of systems are known which attempt to adjust and maintain the radial clearances between the rotor and stator elements throughout all operating conditions of the gas turbine engine. It is known to utilize an air distribution system which, depending upon the gas turbine engine operating conditions, feeds either cooling or heating air onto the rotor and/or stator elements to cause their contraction or expansion. Generally, the air is taken from the air compressor of the gas turbine engine and may be distributed onto turbine blades, turbine wheels, casings, or turbine stator carrier rings. Depending upon the particular objective, air may be tapped from various stages of the compressor, or may be taken from the combustion chamber enclosure to supply the necessary heating air. The air supply systems are typically provided with regulating valves so as to modulate the air flow and the temperatures by mixing air from the different sources.
French Patent Nos. 2,496,753; 2,464,371; 2,431,609; 2,360,750; and 2,360,749 all disclose such air flow systems wherein the air distributors or valves are actuated by means which sense an operational parameter of the gas turbine engine in relation to a measured value, such as temperature, speed of rotation, or the direct measurement of the radial clearance at a particular time. The air flow control valve may also be hydromechanically regulated on the basis of predetermined operational characteristics.
However, in regard to gas turbine engines which demand a more accurate control of the radial clearance during real-time operation of the gas turbine engine, the prior art has not provided satisfactory results. The tapping of air from a compressor stages may degrade the overall engine efficiency according to the prior art systems. Also, for some transient engine operating conditions, regulation of the air control valve by considering only one or, at most, a few of the operational parameters of the gas turbine engine is not sufficient to prevent either excessively large clearances, which may degrade the gas turbine engine performance during acceleration, or excessively small radial clearances which may permit contact between the stator and rotor elements resulting in a reduction in the life of the components.